core: add build skeleton and provisional test harness

Self-contained core/CMakeLists.txt (veloxcore STATIC + velox::core alias),
warnings at target scope so the sanitizer presets' CMAKE_CXX_FLAGS override
doesn't drop -Werror. vtest: ~150-line header-only harness (VT_TEST /
VT_CHECK / VT_REQUIRE / VT_CHECK_EQ) behind a one-function vdm_add_test(),
so the swap to a real framework once PKG picks one is mechanical.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HPPSGhiArbvQgwC2DNiURS

core/tests/CMakeLists.txt

@@ -0,0 +1,22 @@
+# CORE unit tests.
+#
+# Harness is the provisional header-only vtest (support/vtest.hpp); PKG owns the final
+# framework choice (core/docs/pkg-requests-m1.md P2). vdm_add_test() is the only thing
+# test files touch, so swapping harnesses is a one-function edit.
+
+add_library(vtest_main STATIC support/vtest_main.cpp)
+target_include_directories(vtest_main PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/support)
+target_compile_features(vtest_main PUBLIC cxx_std_23)
+
+function(vdm_add_test name)
+    add_executable(${name} ${ARGN})
+    target_link_libraries(${name} PRIVATE veloxcore vtest_main)
+    target_compile_options(${name} PRIVATE -Wall -Wextra -Wpedantic -Werror)
+    add_test(NAME ${name} COMMAND ${name})
+endfunction()
+
+vdm_add_test(veloxcore_result_test    util/result_test.cpp)
+vdm_add_test(veloxcore_event_bus_test util/event_bus_test.cpp)
+vdm_add_test(veloxcore_thread_pool_test util/thread_pool_test.cpp)
+vdm_add_test(veloxcore_bytes_test     util/bytes_test.cpp)
+vdm_add_test(veloxcore_log_test       util/log_test.cpp)